the red and white airport lights that help with your approach angle were working according to the ntsb. >> if the aircraft is too low, all the lights will be red and the way we remember that is red over red you're dead. >> reporter: not working, the guide slope system, a kind of radio beacon that helps bring planes in. we are flying over san francisco and getting a good look at it right now. at the aircraft owners and pilots association in frederick members can actually use a simulator to practice landing at san francisco before they even get there. visually and on instruments. corporate pilot louise beatty said she might glance at her slide scope indicator on a clear day, but she said even without it pilots should have no problem landing safely simply by looking out the window. how big a deal would it be not to have that glide slope? >> none at all. >> reporter: no big deal? >> none at all because you would be relying on visual clues. >> reporter: the precise cause of this crash remains unanswered, but every pilot we have talked to says repairs on sfo's glide slope system should not h